Ground Loops and Insulation for Direct Exchange Geothermal Systems

ABSTRACT

A direct exchange geothermal heating and cooling system has a vacuum insulation layer surrounding the liquid phase working fluid transport line in the system&#39;s ground loop, as well as optional multiple vapor phase working fluid transport lines.

FIELD OF THE DISCLOSURE

The present disclosure relates to geothermal direct exchange (“DX”) heating/cooling systems, which are also commonly referred to as “direct exchange” heating/cooling systems.

BACKGROUND OF THE DISCLOSURE

Geothermal water-source heat exchange systems typically have first and primary fluid-filled closed loops of tubing buried in the ground or submerged in a body of water, to either absorb heat from, or to reject heat into, the naturally occurring geothermal mass and/or water surrounding the buried or submerged fluid transport tubing. The first tubing loop is extended to the surface and circulates the naturally warmed or cooled fluid to an interior heat exchanger, which is in thermal communication with a secondary closed loop heat pump system

Early conventional design geothermal water-source heating/cooling systems typically circulate, via a water pump, a fluid comprised of water, or water with anti-freeze, in plastic (typically polyethylene) underground geothermal tubing to transfer geothermal heat to or from the ground in a first heat exchange step. In a second heat exchange step, a refrigerant heat pump system is used to transfer heat to or from the water. Finally, in a third heat exchange step, an interior air handler (comprised of finned tubing and a fan) is used to transfer heat to or from the refrigerant to heat or cool interior air space.

More recent geothermal DX heat pump heat systems install refrigerant fluid transport lines directly in the sub-surface ground and/or water and typically circulate, via the system's compressor, a refrigerant fluid (such as R-22, R-407C, R-410A, or the like) within the sub-surface refrigerant transport lines (which lines are typically comprised of copper tubing) to transfer geothermal heat to or from the sub-surface elements via a first heat exchange step. DX systems only require a second heat exchange step to transfer heat to or from the interior air space, typically by means of an interior air handler. Consequently, DX systems are generally more efficient than water-source systems because fewer heat exchange steps are required and because no water pump energy expenditure is necessary. Further, since copper is a better heat conductor than most plastics, and since the refrigerant fluid circulating within the copper tubing of a DX system generally has a greater temperature differential with the surrounding ground than the water circulating within the plastic tubing of a water-source system, less excavation and drilling are typically required and installation costs are lower.

While most in-ground/in-water DX heat exchange designs are feasible, various improvements have been developed intended to enhance overall system operational efficiencies. Several such design improvements, particularly in direct expansion/direct exchange geothermal heat pump systems, are taught in U.S. Pat. No. 5,623,986 to Wiggs; in U.S. Pat. No. 5,816,314 to Wiggs, et al.; in U.S. Pat. No. 5,946,928 to Wiggs; in U.S. Pat. No. 6,615,601 B1 to Wiggs; and in U.S. Pat. No. 6,932,149 to Wiggs, the disclosures of which are incorporated herein by reference. Such disclosures encompass both horizontally and vertically oriented sub-surface heat geothermal heat exchange means.

SUMMARY OF THE DISCLOSURE

In any particular DX heat pump system design, increasing system operational efficiencies and/or reducing initial installation expenses are of paramount importance. The subject matter disclosed herein primarily relates to various DX system design improvements that will increase system operational efficiencies and/or that will help to reduce initial ground loop installation costs of a DX system.

The direct exchange geothermal methods and systems disclosed herein increase DX heat pump system operational efficiencies and/or to help reduce DX heat pump system initial installation costs/expenses by providing enhanced efficiency DX heat pump system working fluid containment ground loop insulation designs (a vacuum insulation) and an optional simultaneous improved ground loop multiple vapor phase refrigerant transport line design. These features may improve operational performance and/or may reduce costs for installing DX systems.

The working fluid ground loop portion of DX heat pump systems generally include containment tubing comprised of metal (usually copper), although other materials may optionally be utilized. The ground loops may be installed within the surrounding geology and may optionally be installed within a casing of a well formed in the surrounding geology, as is well understood by those skilled in the art. The transport containment loop of a DX system is a closed loop. The closed loop is comprised of a refrigerant transport line loop. For a reverse-cycle DX heating and cooling system with the primary ground loop portion installed within a well, or the like, the well is typically vertically oriented and/or downwardly angled. After insertion of the ground loop within the well, the remaining empty annular space within the well may then be filled with a heat conductive grout fill material (typically a heat conductive grout fill material).

The ground loop is typically comprised of one larger-sized vapor transport line that is coupled, at/near the bottom of the well, to one smaller-sized liquid transport line. The sub-surface portion of the ground loop provides an exterior heat exchanger that transfers heat to and from the working fluid circulated (by the heat pump compressor) within loop to and from the surrounding geology adjacent to the loop, which loop is itself within a heat conductive fill material or other solid-state element (sometimes water) within the well. The heat is transferred to and from a working fluid circulating within the transport tubing (usually copper tubing). The heat conductive fill material may be formed of a fluid, a liquid (such as water and/or antifreeze, or the like), a solid (such as a cementitious grout, or the like), a gel, a mixture of bentonite clay, sand, and water, water alone, or any other heat conductive fill material.

Various DX heat pump system containment ground loop designs have been disclosed by U.S. Pat. No. 5,623,986 to Wiggs, by U.S. Pat. No. 5,816,314 to Wiggs, et al, and by U.S. Pat. No. 6,932,149 B2 to Wiggs. Wiggs' 149 discloses a means for operating a reverse-cycle DX system in conjunction with such DX system ground loop designs by providing, respectively, a smaller liquid refrigerant transport line and a larger vapor refrigerant transport line.

In any DX heat pump system subsurface ground loop design where there is at least one vapor transport line and at least one liquid transport line within the same well, even when the liquid line is insulated with any solid-state insulation material (such as polyethylene and/or expanded polyethylene foam and/or rubber foam, or the like), as has historically always been the case, there is some “short-circuiting” heat transfer among the two respective transport lines (the typically warmer vapor line and the typically cooler liquid line) within the same well. Any such “short-circuiting” heat transfer is disadvantageous to overall system operational efficiencies. Historically, most, if not all, DX systems with ground loops installed within vertically and/or downwardly angled wells utilize only one smaller sized liquid phase transport line and only one larger sized vapor phase transport line, where the size is determined via the cross-sectional area of the interior of the respective fluid transport lines.

Although the DX industry has historically anticipated and assumed that the provision of a solid-state insulation material surrounding at least some portion of the ground loop's refrigerant working fluid liquid phase transport line is adequate, extensive field testing and analysis has demonstrated that a vastly improved method of providing a vacuum insulation for the liquid line in any ground loop design for any DX system may significantly improve system operational efficiencies, as utilization of a vacuum insulation provides an approximate eight to ten times insulation value over that of solid-state insulation types previously utilized. Namely, the working fluid (a refrigerant, such as R-407C, R-22, R-410A, R-134A, CO2, or the like, in a DX system application) would have a liquid return line that would be insulated by a surrounding housing, or the like, with a vacuum being pulled between the exterior surface of the liquid return line and the interior surface of the surrounding housing used for insulation purposes. The vacuum may be pulled to at least a 1,000 micron level.

Further, the herein disclosed vacuum insulation maximizes system value (by reducing initial system installation costs), in that extensive testing and analysis has demonstrated that when such a vacuum insulation is utilized, historical well depths for DX systems can be reduced by about 50%. This means the cost of drilling and grouting for DX systems can be reduced by about 50%. The cost of drilling and grouting is typically the most expensive part of any geothermal system installation.

For example, with conventional water-source geothermal systems, typically about 150 to 250 feet per ton of system design capacity is historically required in well depth. However, with a DX system, historically, only about 100 to 120 feet per ton of system design capacity is required in well depth. Thus, historically, DX systems have required less drilling and grouting than water-source systems. This is generally because of: one-third less heat transfer steps required by a DX system (as previously explained); because of better heat transfer to the surrounding geology through a DX system's subsurface metal tubing instead of through a water-source system's subsurface plastic tubing; because of a DX system's higher temperature differentials between its circulating sub-surface working fluid and the surrounding geology than that of a water-source system; and because of a DX system's working fluid's (typically a refrigerant) phase change ability, which permits it to reject/absorb more BTUs per pound of working fluid than a water-source system under typical geological temperature conditions within about 500 feet of the surface.

However, with a DX system vacuum insulated liquid line in the ground loop, such as where the vacuum insulation surrounds at least about 30% of the upper portion of the liquid line in the ground loop, only about 50 to 60 feet of well depth is needed per ton of system design capacity. About at least 90% of the upper portion of the liquid line in the ground loop may be vacuum insulated when the system is operating in one of the cooling mode and a reverse-cycle mode (alternating heating and cooling modes). Thus, in a DX system design with a vacuum-insulated liquid line in its sub-surface ground loop, the reduction in drilling and grouting requirements is about 50% over that of conventional DX system ground loop designs requiring about 100 to 120 feet per ton of system design capacity. As drilling and grouting costs can currently run about $15 (USA$) per foot of depth, or more, this is an extremely important and critical factor in decisions regarding financial cost and payback implications.

However, extensive testing has also demonstrated that while the well depth may be dramatically reduced, as explained, and while the length of the vacuum insulated liquid working fluid transport line in the ground loop may be correspondingly reduced, the original design length of the vapor working fluid transport line must be maintained. Therefore, testing has shown that, in conjunction with a shortened vacuum insulated liquid line in a DX system ground loop, at least two vapor phase refrigerant/working fluid transport lines may be installed within the same well so that the original total design length of the un-insulated and thermally exposed vapor line is maintained. For example, if an original DX system well depth design and corresponding ground loop length was 100 feet per ton with conventional solid-state insulation surrounding some portion of the liquid line, with the newly herein disclosed vacuum insulated liquid line design of the system's ground loop, at least one 50 foot vacuum insulated liquid line may be utilized, but in conjunction with at least two 50 foot un-insulated vapor lines, all within the same well. While testing has shown that at least one 50 foot vapor line may optionally be utilized when the vapor line's interior cross-sectional area (of the one original 100 foot vapor line) is doubled, testing has also shown that the use of at least two respective 50 foot lines provides superior operational results due to the larger total surface area exposure to surrounding geological geothermal temperatures.

The housing surrounding the liquid phase transport line within the well that is utilized for vacuum insulation purposes may itself be optionally comprised of a poor heat conductive material, such as polyethylene, or the like, so that if any portion of the inner working fluid transport line touched the surrounding housing, direct conductive thermal heat transfer would be minimized. Additionally and/or alternately, the inner liquid phase transport line may be relatively (not necessarily exactly) centered, via spacers, such as nubs or the like, within the surrounding insulating housing, to help prevent or minimize disadvantageous thermal contact between the exterior wall of the inner liquid phase transport line and the interior wall of the housing. Alternatively, the inner liquid transport line may have at least one of an expanded foam and a solid-state insulation surrounding it within the space between the exterior surface of the liquid transport line and the interior surface of the housing (in the same area/space as where the vacuum is pulled for superior insulation purposes), to help prevent direct material thermal contact therebetween.

The exposed heat transfer vapor transport line within the well would fluidly communicate (typically at least one of at and near to the bottom of the well) with the smaller liquid transport line, at least some portion of which (generally at least about 33%) liquid transport line would be situated within the surrounding vacuum insulation housing. All of the vapor transport lines, the liquid transport line, and the surrounding housing, may optionally be situated within at least one of a well and a containment pipe within a well, where the containment pipe (such as a pipe comprised of at least one of a metal and a heat conductive casing) is optionally filled with one of a heat conductive grout, gel, or water, and where the exterior or the containment pipe would be surrounded by at least one of earth, water, and a heat conductive fill material, such as a heat conductive grout.

The entire assembly may optionally also be comprised of a DX system ground loop design, with a smaller centrally located vacuum insulated liquid transport line, where the insulation housing is surrounded by one or more spiraled exposed (meaning non-insulated) larger vapor refrigerant transport lines and/or at least one vertically oriented exposed (meaning non-insulated) larger vapor line. However, testing has also indicated that at least two vapor phase transport lines installed within the same well and/or containment pipe, along with the vacuum insulated liquid phase transport line, may provide superior results to that of a single vapor line of an equivalent total interior cross-sectional area, due to the enhanced surface area exposure provided by the at least two respective vapor transport lines.

The subject designs with the vacuum insulated central return line could also be utilized as a sub-surface heat exchanger in a traditional water-source geothermal heat pump system, where the working fluid (circulating within what is referred to as vapor and liquid lines in a DX system design) would be one of water and antifreeze instead of a refrigerant, which refrigerant would only be utilized as the working fluid in a DX system. Further, in a DX system design, or in any other geothermal heat pump design, the use of a vacuum insulation for insulating at least one of the vapor line and the liquid line in at least one of near-surface trenching and in above-ground refrigerant transport tubing may be advantageous.

An evacuated space comprising a vacuum may be created using a vacuum pump. Typically, a vacuum pump line is connected (to the area between the exterior wall of the inner liquid phase refrigerant transport line and the interior wall of the surrounding secondary line) by a Shrader valve, or the like. The vacuum pump is operably attached to the Shrader valve and a vacuum is pulled. When the desired vacuum level is achieved, the vacuum pump is removed from the Shrader valve and a screw type cap may be placed over the top of the valve as a precautionary extra seal. Historically, vacuums are typically pulled in the HVAC industry to evacuate non-condensable air in refrigerant systems, and have not heretofore been pulled for insulating the liquid transport line in a DX system. However, as explained, extensive testing has demonstrated that the provision of a vacuum insulation for at least some portion of the liquid line in a DX system ground loop is a critical to the provision of actual enhanced system operational efficiencies increases in at least one of Coefficient Of Performance (COP) and capacities (BTU production levels). The vacuum insulation for at least some portion of the liquid line in a DX system ground loop may include at least ninety percent of the liquid line within the ground loop being vacuum insulated.

While vapor phase and liquid phase transport lines are respectively referred to herein, it should be understood that the respective lines are designed to respectively transport mostly liquid phase and mostly vapor phase refrigerant, but there may periodically be some vapor in the liquid line and that there may periodically be some liquid in the vapor line.

A basic closed loop direct exchange geothermal heating/cooling heat pump system (not specifying refrigerant expansion devices, reversing valves, controls, wiring, etc., all of which are well understood to typically be included in DX heat pump systems by those skilled in the art) with a vacuum insulated sub-surface liquid line is herein defined as comprising:

a refrigerant working fluid including a liquid phase refrigerant transport tubing operably coupled to a vapor phase refrigerant transport tubing, together with a sub-surface portion of the vapor tubing defining an exterior geothermal DX system heat exchanger;

at least one sub-surface portion of liquid tubing that, in conjunction with a coupled portion of sub-surface vapor tubing, defines a sub-surface ground loop of a DX system heat exchanger;

a vacuum insulation surrounding at least 30% of the upper portion of the sub-surface liquid tubing (testing has also indicated that surrounding at least 90% of the upper portion of the sub-surface liquid refrigerant transport tubing may be advantageous, especially when utilized in one of a cooling mode and a reverse-cycle system mode of operation);

at least one compressor that both compresses and circulates the refrigerant working fluid through the DX heat pump system, inclusive of through the sub-surface vapor and liquid tubing; and

an interior heat exchanger disposed within the closed refrigerant tubing transport loop (an interior heat exchanger may be comprised of an air handler, a refrigerant to water heat exchanger, or the like, as is well understood by those skilled in the art).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a liquid transport line that is surrounded by a solid-state insulating material, and where both the liquid line and its solid-state insulating material are both contained within an outer housing, with a vacuum insulation in the empty annular space between the exterior surface of the solid-state insulating material and the interior surface of the outer housing.

FIG. 2 is a side view of a liquid transport line having exterior nubs, and where both the liquid line and nubs are contained within an outer housing, with a vacuum insulation in the empty annular space between the exterior surface of the solid-state insulating material and the interior surface of the outer housing, and with an access valve to facilitate the pulling of a vacuum.

FIG. 3 is a side view of a liquid transport line surrounded by a solid-state insulating material, and where both the liquid line and its solid-state insulating material are contained within an outer housing, with a vacuum insulation in the empty annular space between the exterior surface of the solid-state insulating material and the interior surface of the outer housing, and with an access valve to facilitate the pulling of a vacuum.

FIG. 4 is a side view of a liquid transport line with nubs on its exterior wall surrounded by an outer housing, with a vacuum insulation in the empty annular space between the exterior surface of the liquid transport line and the interior surface of the outer housing, and where there are two non-insulated and thermally exposed vapor transport lines operably connected to the liquid transport line, all within a grout-filled well.

FIG. 5 is a side view of a liquid transport line surrounded by a radiant heat insulating material, where both the liquid line and radiant heat insulating material are contained within an outer housing, where gas absorbing pellets are disposed within the space between the exterior surface of the radiant heat insulating material and the interior surface of the outer housing, and where there are spacers separating the liquid transport line and the outer housing.

FIG. 6 is a side view of a vacuum insulated liquid transport line surrounded by an outer housing, where a vacuum insulation exists within the empty annular space between the exterior surface of the liquid phase transport line and the interior surface of the outer housing, where a vapor transport line is spiraled around the outer housing, and where the spiraled vapor phase line is inserted within an enclosure with the enclosure's remaining empty annular space filled with a heat conductive fill material.

DETAILED DESCRIPTION

The following detailed description is of the best presently contemplated mode of carrying out the subject matter disclosed herein. The description is not intended in a limiting sense, and is made solely for the purpose of illustrating the general principles of this subject matter. The various features and advantages of the present disclosure may be more readily understood with reference to the following detailed description taken in conjunction with the accompanying drawings.

Referring now to the drawings in detail, where like numerals refer to like parts or elements, there is shown in FIG. 1 a top view of a liquid phase working fluid transport line 1 that is surrounded by a solid-state insulating material layer 3. Both the fluid transport line 1 and solid-state insulating material 3 are contained within an outer housing 2, with a vacuum insulation 4 in the empty annular space between the exterior surface of the solid-state insulating material 3 and the interior surface of the outer housing 2. While a vacuum is not shown, the empty space in which the vacuum insulation is formed exists is identified as a vacuum chamber 4. In some embodiments, the vacuum chamber 4 may be placed at a vacuum level of at least one thousand microns to provide a desired level of insulation around the fluid transport line 1.

The outer housing 2 surrounding the liquid line 1 and its solid-state insulating material 3 may itself be comprised of a poor heat conductive material, such as polyethylene for example. When the outer housing 2 surrounding the liquid line 1 is comprised of a poor heat conductive material, the provision of a solid-state insulating material 3 surrounding the liquid line 1 is optional and may not be necessary.

The liquid line 1, solid-state insulating material 3, and outer housing 2 with vacuum insulation in vacuum chamber 4 are all shown herein as an example of a sub-surface portion of a geothermal direct exchange (DX) heat pump system. DX heat pump systems, which are not shown herein in any detail as same are well understood by those skilled in the art, are generally comprised of a sub-surface heat exchanger, a compressor box, and an interior heat exchanger (such as an air handler for one example). The subject disclosures herein primarily relate to the sub-surface heat exchanger portion of a DX heat pump system.

FIG. 2 is a side view of a liquid transport line 1 having nubs 5, or the like, attached to the exterior surface of the liquid transport line 1. Both the liquid transport line 1 and nubs 5 are contained within an outer housing 2, with a vacuum pressure formed in the vacuum chamber 4.

An access valve 6, such as a Shrader valve or the like, is attached to an upper sealed portion 7 of a vacuum insulation encasement assembly 8 to facilitate the pulling of a vacuum within the vacuum chamber 4, which encasement assembly 8 also has a lower sealed portion 9. Access valves 6, such as Shrader valves or the like, are well understood by those skilled in the art.

The vacuum insulation encasement assembly 8 forms a completely sealed vacuum chamber 4 between the upper sealed portion 7 and the lower sealed portion 9, where the liquid transport line 1 is respectively attached to the outer housing 2 that surrounds it, so that a vacuum pressure may be pulled and held within the vacuum chamber 4.

FIG. 3 is a side view of a liquid transport line 1 that is surrounded by a solid-state insulating material 3. Here, both the liquid line 1 and solid-state insulating material 3 are contained within an outer housing 2, with a vacuum insulation formed in the vacuum chamber 4, and with an access valve 6, such as a Schrader valve or the like, to facilitate the pulling of a vacuum within an encasement assembly 8. The encasement assembly 8 has an upper sealed portion 7 and a lower sealed portion 9 to provide a completely sealed vacuum chamber 4.

FIG. 4 is a side view of a liquid phase working fluid transport line 1 with nubs 5 on its exterior wall to help prevent any significant disadvantageous thermal contact between the liquid line 1 and its surrounding outer housing 2. A vacuum insulation is pulled within the vacuum chamber 4. Here, the vacuum chamber 4 is shown as extending from the top down to a point near the bottom 18 of the 13 well, so that at least about ninety percent of the liquid transport line 1 is surrounded with vacuum insulation, for use in at least one of the cooling mode of system operation and a reverse-cycle mode of system operation (meaning the system periodically switches between the cooling mode and the heating mode). If utilized in a heating mode only application, the vacuum insulation may only extend about thirty percent of the way down the liquid line 1 from the top of the well 13.

Here, there are two respective non-insulated and thermally exposed vapor transport lines 10 operably connected to the liquid transport line 1 via a distributor 11 and respective couplings 12, all within a well 13 filled with a heat conductive fill material 14, such as a grout, or the like. The heat conductive fill material 14 helps to insure good thermal heat transfer between the vapor phase refrigerant transport lines 10 and the geology 20 surrounding the well 13. While a well 13 is shown herein, some portion of the well 13 may be cased (typically with a good heat conductive steel casing). Thus, the well 13 shown herein could also optionally represent well casing.

The liquid line 1 and nubs 5 are contained within an outer housing 2, with a vacuum insulation formed in the vacuum chamber 4, and with an access valve 6, such as a Schrader valve or the like, to facilitate the pulling of a vacuum within an encasement assembly 8, The encasement assembly 8, has an upper sealed portion 7 and a lower sealed portion 9.

The encasement assembly 8 represents a full and complete sealed vacuum chamber 4 between the upper sealed portion 7 and the lower sealed portion 9, where the liquid line 1 is respectively attached to the outer housing 2 that surrounds it, so that a vacuum pressure may be pulled and held within the vacuum chamber 4.

Although not shown herein in detail, it is well understood by those skilled in the art that there are commonly termed near surface “line sets” extending from the well 13 to the interior DX system equipment, such as the compressor box. It is also well understood by those skilled in the art that above-ground “line sets’ also typically extend from the compressor box to the interior heat exchanger, which is typically an air handler. Such “line sets” are typically comprised of a liquid line 1 and at least one vapor line 10. As the use of a vacuum insulation has proven to be advantageous in a DX system application, one may also independently and respectively vacuum insulate at least one of the liquid line and the vapor line respectively situated in at least one of near-surface line sets and in above-ground line set locations.

FIG. 5 is a side view of a liquid transport line 1 surrounded by a radiant heat insulating material 15, where both the liquid line 1 and radiant heat insulating material 15 are surrounded by an outer housing 2. The outer housing 2 may be constructed of at least one of a metal and of a poor heat conductive material, such as polyethylene or the like (as an example).

Here, there are gas absorbing pellets 16, or the like, disposed within the vacuum chamber 4. The gas absorbing pellets 16 may absorb gas emissions from at least one of materials (materials utilized in the construction/composition of at least one of the liquid phase working fluid transport line, the radiant heat insulating material 15, and the outer housing 2) and from gas infiltration (not shown herein, but such as hydrogen gas, or the like, that could infiltrate the wall of the outer housing 2) to maintain a good vacuum insulation within the vacuum chamber 4.

Here, spacers 17 separating the liquid transport line 1 and the outer housing 2 are shown as another example of a separating means (other than nubs shown as 5 for an optional example in FIGS. 2 and 4).

FIG. 6 is a side view of a vacuum insulated liquid transport line 1 surrounded by an outer housing 2, where a vacuum insulation has been pulled within the vacuum chamber 4.

Here, as an optional DX system ground loop construction example, a thermally exposed and un-insulated vapor transport line 10 is shown spiraled around the outer housing 2. The vapor line 10 is operably connected to the liquid line 1 by means of a coupling 12 situated at or near the bottom 18 of an enclosure 19 having a thermally heat conductive exterior wall. The vacuum insulated liquid transport line 2 and spiraled vapor phase line 10 are all herein shown as being inserted and contained within the enclosure 19.

The remaining empty annular space within the enclosure 19 between the exterior surface of the outer housing 2 and the interior surface of the enclosure 19 is filled with a heat conductive fill material 14, such as a grout, so as to effect good thermal heat transfer between the refrigerant working fluid within the vapor phase line 10 and the surrounding geology 20. An access valve 6, such as a Schrader valve or the like, is shown to facilitate pulling a vacuum within an encasement assembly 8 (an encasement assembly 8 is more fully described above in FIGS. 2 and 4). 

What is claimed is:
 1. A direct exchange geothermal heat pump for use with a sub-surface formation, comprising: a closed loop for transporting a working fluid, the closed loop including: a liquid transport line including a liquid transport line sub-surface portion; and a vapor transport line including a vapor transport line sub-surface portion fluidly communicating with the liquid transport line sub-surface portion and positioned in thermal conductive relation with the sub-surface formation to provide an exterior heat exchanger; wherein the liquid transport line sub-surface portion and the vapor transport line sub-surface portion define a closed sub-surface ground loop; and a vacuum insulation assembly surrounding at least an upper portion of the liquid transport line sub-surface portion to define a vacuum-insulated portion of the liquid transport line sub-surface portion.
 2. The direct exchange geothermal heat pump of claim 1, in which the vacuum insulation assembly comprises a housing surrounding the vacuum-insulated portion of the liquid transport line sub-surface portion to define a vacuum chamber between an interior surface of the housing and an exterior surface of the vacuum-insulated portion of the liquid transport line sub-surface portion, and a vacuum pressure formed in the vacuum chamber.
 3. The direct exchange geothermal heat pump of claim 2, in which the exterior surface of the vacuum-insulated portion of the liquid transport line sub-surface portion is spaced from the housing interior surface.
 4. The direct exchange geothermal heat pump of claim 3, further comprising a solid-state insulation material disposed between the exterior surface of the vacuum-insulated portion of the liquid transport line sub-surface portion and the housing interior surface.
 5. The direct exchange geothermal heat pump of claim 3, further comprising nubs or spacers disposed between the exterior surface of the vacuum-insulated portion of the liquid transport line sub-surface portion and the housing interior surface.
 6. The direct exchange geothermal heat pump of claim 1, in which the vacuum pressure comprises a vacuum pressure level of at least 1,000 microns.
 7. The direct exchange geothermal heat pump of claim 2, further comprising gas absorbing pellets disposed within the vacuum chamber.
 8. The direct exchange geothermal heat pump of claim 1, further comprising a radiant heat transfer insulation layer disposed around the vacuum-insulated portion of the liquid transport line sub-surface portion.
 9. The direct exchange geothermal heat pump of claim 1, in which the vapor transport line sub-surface portion comprises at least two distributed vapor transport lines.
 10. The direct exchange geothermal heat pump of claim 2, in which the housing is formed of a housing material having poor heat conductivity.
 11. The direct exchange geothermal heat pump of claim 10, in which the housing material comprises polyethylene.
 12. The direct exchange geothermal heat pump of claim 1, in which the vacuum-insulated portion of the liquid transport line sub-surface portion comprises at least 30% of an overall length of the liquid transport line sub-surface portion.
 13. The direct exchange geothermal heat pump of claim 1, in which The direct exchange geothermal heat pump is operable in a cooling mode or a reverse cycle mode, and in which the vacuum-insulated portion of the liquid transport line sub-surface portion comprises at least 90% of an overall length of the liquid transport line sub-surface portion.
 14. The direct exchange geothermal heat pump of claim 1, in which the liquid transport line and the vapor transport line define a transport line set positioned near or above a ground surface, and in which at least a portion of the transport line set is surrounded by a vacuum insulation. 